Thermoplastically processable polyurethane—which will be referred to as TPU below—is a material that has proven successful as a sheath material in the cable industry due to its excellent properties. The material is highly abrasion resistant, has high thermal stability, and can be made flame-resistant to self-extinguishing by adding certain materials. Cable sheaths made of polyurethane exhibit resistance to cutting, initial tearing, and tear propagation. In addition, polyurethane is or can be formulated to be resistant to ozone, microbes, oil, and high-energy radiation. Cables equipped with a polyurethane sheath are extremely flexible and can withstand high numbers of bending cycles over tight radii.
However TPU has a mostly undesirable characteristic in that it forms a relatively thin melt at elevated temperatures. In case of fire, this has the effect that the liquid material drips off and the cable core is thus exposed. At extremely high temperatures, the materials added to improve flame-resistance are frequently inadequate, and burning or hot material drips and, under some circumstances, ignites other material, thereby causing a rapid expansion of fire.
It is an object of the present invention to provide a formulation comprising at least one TPU, which formulation has less tendency to drip or even does not drip in case of fire and has excellent flame retardancy.